Cushioning sheet for use in denture casting

Abstract

A cushioning sheet made of a flammable material for use, e.g. in denture casting. It is inserted into a casting frame and adapted to burn out when heated to leave a space between a casting frame and a casting mold in the frame. The space serves to absorb the difference in the thermal expansion between the frame and the mold, thus preventing the casting mold from cracking or breaking. The cushioning sheet is formed with apertures. The casting material penetrates through the apertures, abutting against the casting frame to support the casting mold upon the frame even after the cushioning sheet has burnt out.

What is claimed is: 
     
       1. In combination, a lost wax casting process casting frame and a cushioning sheet for covering substantially the entire inner periphery of said casting frame used in a lost wax casting process, said cushioning sheet for being placed between a casting material and said casting frame for absorbing both the expansion of the casting material when hardening in said casting frame and the difference in the rates of thermal expansion between the hardened casting material and said casting frame when said casting frame and hardened casting material are heated to burn out said cushioning sheet, said cushioning sheet comprising: a substantially planar layer of flammable materials;   a plurality of through apertures in said substantially planar layer of flammable material, each one of said plurality of apertures being of a predetermined size relative to the area of said layer of planar material for causing the non-apertured area of said layer of planar material to absorb the force of expansion of the casting material when hardening in said casting frame and to define a space determined by the volume of the non-apertured area to absorb the difference in the rates of thermal expansion between the hardened casting material and said casting frame when said casting frame and the hardened casting material are heated to burn out said layer of planar material, and said predetermined size of said plurality of apertures allowing a portion of the casting material to enter said plurality of apertures and contact said casting frame for forming a sufficient number of predetermined areas of contact between the hardened casting material and said casting frame for retaining the hardened casting material in said casting frame after said layer of casting material has been burned out.   
     
     
       2. A device as in claim 1, wherein said plurality of apertures includes rectangular and square apertures. 
     
     
       3. A device as in claim 2, wherein said plurality of apertures is in a latticed pattern. 
     
     
       4. A device as in claim 3, wherein said flammable layer of planar material burns at 700° to 800° C. 
     
     
       5. A device as in claim 4, wherein said flammable layer of planar material is one of the group consisting of vinyl chloride, polyethylene, and paper.